1. mRNA expression and binding sites for alpha2-adrenergic receptor subtypes in muscle layers of the ileum and spiral colon of dairy cows.
- Author
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Ontsouka EC, Blum JW, Steiner A, and Meylan M
- Subjects
- Animals, Cattle genetics, DNA Primers, Female, Idazoxan analogs & derivatives, Protein Binding, Reverse Transcriptase Polymerase Chain Reaction, Tritium, Cattle metabolism, Lower Gastrointestinal Tract metabolism, Muscle, Smooth metabolism, RNA, Messenger metabolism, Receptors, Adrenergic, alpha-2 metabolism
- Abstract
Objective: To measure maximum binding capacity (B(max)) and levels of mRNA expression for alpha(2)-adrenergic receptor (AR) subtypes in ileal and colonic muscle layers of healthy dairy cows., Sample Population: Ileal and colonic muscle specimens from 6 freshly slaughtered cows., Procedures: Ileal and colonic muscle layers were obtained by scraping the mucosa and submucosa from full-thickness tissue specimens. Level of mRNA expression for alpha(2)-AR subtypes was measured by real-time reverse transcriptase-PCR analysis and expressed relative to the mean mRNA expression of glyceraldehyde phosphate dehydrogenase, ubiquitin, and 18S ribosomal RNA. Binding studies were performed with tritiated RX821002 ((3)H-RX821002) and subtype-selective ligands as competitors., Results: mRNA expression for alpha(2AD)-, alpha(2B)-, and alpha(2C)-AR subtypes was similar in ileal and colonic muscle layers. The mRNA expression for alpha(2AD)-AR was significantly greater than that for alpha(2B)- and alpha(2C)-AR subtypes, representing 92%, 6%, and 2%, respectively, of the total mRNA. Binding competition of (3)H-RX821002 with BRL44408, imiloxan, and MK-912 was best fitted by a 1-site model. The B(max) of alpha(2AD)- and alpha(2C)-AR sub-types was greater than that of alpha(2B)-AR. The B(max) and level of mRNA expression were only correlated (r = 0.8) for alpha(2AD)-AR. Ratio of B(max) to mRNA expression for alpha(2C)-AR was similar to that for alpha(2B)-AR, but significantly greater than for alpha(2AD)-AR., Conclusions and Clinical Relevance: Subtypes of alpha(2)-AR in bovine intestinal muscle layers are represented by a mixture of alpha(2AD)- and alpha(2C)-ARs and of alpha(2B)-AR at a lower density. Information provided here may help in clarification of the role of AR subtypes in alpha(2)-adrenergic mechanisms regulating bovine intestinal motility.
- Published
- 2006
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